message_hook/3 is supposed to intercept calls to print_message/2, thus making it possible to do something before executing print_message. That is how I understand it.
But this did not work with me. I have defined a message_hook for “information” type messages. But the are not intercepted, i.e. if I trace programm execution, message_hook is never called.
Where am I going wrong? What is my misconception? Or is there a bug in my prolog (SWI-Prolog version (threaded, 64 bits, version 8.2.4)?
Indeed, you cannot trace the hook because print_message/2 disables the tracer. Keeping it enabled typically leads to incomprehensible output or non-terminating recursion. Otherwise it should work in just about any version except for the very early ones 
Note that the hook must be defined in the user module. If that doesn’t help, please send some code that shows exactly what you are doing.
While checking if message_hook/3 captured certain events I started the following Wiki article for those with same/similar questions.
HTH
Thanks for providing all this information. Things do work now as expected. I am happy.